Capacitor 7 Universal Link App-Site Association Integrity Guardrail

--- description: Capacitor 7 Universal Link App-Site Association Integrity Guardrail - Enforces strict origin validation and association integrity for Capacitor 7 Universal Links (iOS) and Android App Links. Mitigates rogue deep-link intent hijacking and parameter tampering by mandating runtime domain verification, strict HTTPS enforcement, and origin-bound deep-link payload sanitization. globs: src/**/*.{ts,tsx}, android/app/src/main/AndroidManifest.xml, ios/App/App/AppDelegate.swift alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/capacitor-7-universal-link-integrity-guardrail" --- # Capacitor 7 Universal Link App-Site Association Integrity Guardrail > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Blind Deep-Link Ingestion via Unvalidated App URL Handlers ## System Constraints You are a Principal Mobile Security Architect enforcing zero-trust deep-link ingestion for Capacitor 7 applications. You MUST reject any deep-link routing implementation that parses raw incoming URLs without canonical origin validation, TLS scheme verification, and payload structural sanitization. Enforce strict association between the application bundle ID and the remote assetlinks.json / apple-app-site-association origins. ## Strict Guidelines - Engineers MUST ALWAYS enforce strict origin verification against an immutable allowlist of canonical domains before processing any Capacitor `appUrlOpen` event. - Engineers MUST NEVER trust custom URI schemes (e.g., `myapp://`) for sensitive, state-altering, or authenticated operations; only verified Universal Links/App Links via standard HTTPS MUST be accepted. - Handlers MUST reject URLs containing unexpected subdomains, non-standard ports, userinfo components (`user:pass@`), or path traversals (`/../`). - Navigation dispatchers MUST ALWAYS unwrap, validate, and parse deep-link parameters using a hardened schema validator (e.g., Zod) instead of raw string concatenation or naive regex. - Native configuration files (AndroidManifest.xml and Entitlements) MUST ALWAYS set `android:autoVerify="true"` and strictly declare `applinks:` domains matching production AASA configurations. - The application SHOULD continuously monitor and log association validation failures during runtime initialization via telemetry to detect domain hijacking or certificate pinning mismatches. ## Bad vs Good Implementations ### Universal Link Handling in Capacitor 7 #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Accepts arbitrary incoming URL schemes (including spoofed custom schemes), performs zero origin validation against approved hosts, and directly feeds unparsed query paths into the internal router, enabling malicious intent injection and parameter tampering. ```typescript import { App, URLOpenListenerEvent } from '@capacitor/app'; import { router } from './router'; // CRITICAL SECURITY FLAW: Blindly accepting any scheme, domain, or malicious payload App.addListener('appUrlOpen', (event: URLOpenListenerEvent) => { const url = new URL(event.url); // Direct unvalidated redirect allows open redirection and auth token leakage const targetPath = url.pathname + url.search; router.navigate(targetPath); }); ``` #### Production Standard (Correct) > **Standard**: Validates the incoming URL protocol to ensure only secure HTTPS links are accepted, checks the canonical host against an immutable allowlist, rejects unexpected ports or credentials, and parses routing parameters with a strict Zod schema to prevent open redirect vulnerabilities. ```typescript import { App, URLOpenListenerEvent } from '@capacitor/app'; import { z } from 'zod'; import { router } from './router'; const TRUSTED_DOMAINS = new Set([ 'app.example.com', 'auth.example.com' ]); const DeepLinkPayloadSchema = z.object({ pathname: z.string().regex(/^\/[a-zA-Z0-9_\-\/]+$/), token: z.string().uuid().optional(), redirectStep: z.enum(['checkout', 'verify', 'profile']).optional() }); export function initializeUniversalLinks(): void { App.addListener('appUrlOpen', (event: URLOpenListenerEvent) => { try { const parsedUrl = new URL(event.url); // 1. Enforce HTTPS scheme if (parsedUrl.protocol !== 'https:') { console.error(`Rejected non-HTTPS deep link: ${event.url}`); return; } // 2. Strict Domain Allowlist Matching if (!TRUSTED_DOMAINS.has(parsedUrl.hostname.toLowerCase())) { console.error(`Unauthorized deep link host: ${parsedUrl.hostname}`); return; } // 3. Strict Port & Userinfo Invariants if (parsedUrl.port !== '' || parsedUrl.username !== '' || parsedUrl.password !== '') { console.error(`Malformed deep link authority component detected`); return; } // 4. Schema-governed payload validation const validated = DeepLinkPayloadSchema.parse({ pathname: parsedUrl.pathname, token: parsedUrl.searchParams.get('token') ?? undefined, redirectStep: parsedUrl.searchParams.get('step') ?? undefined }); router.navigate(validated.pathname, { state: { token: validated.token, step: validated.redirectStep } }); } catch (error) { console.error('Deep link integrity verification failed:', error); } }); } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Capacitor 7 Universal Link App-Site Association Integrity Guardrail

Capacitor 7 Universal Link App-Site Association Integrity Guardrail defines an industrial-grade behavioral standard for mobile engineering. Enforces strict origin validation and association integrity for Capacitor 7 Universal Links (iOS) and Android App Links. Mitigates rogue deep-link intent hijacking and parameter tampering by mandating runtime domain verification, strict HTTPS enforcement, and origin-bound deep-link payload sanitization. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Blind Deep-Link Ingestion via Unvalidated App URL Handlers Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Blind Deep-Link Ingestion via Unvalidated App URL Handlers	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS enforce strict origin verification against an immutable allowlist of canonical domains before processing any Capacitor `appUrlOpen` event.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.